The present invention relates to a method and a system for position management of mobile stations in a cellular mobile telephone system.
In order to get possibility to connect incoming calls or transmit data to a mobile station in a cellular mobile system, it is very important that the system can locate or determine the position for the mobile station. The procedure or the function to keep count of the position of a mobile station within the mobile system is in the trade called xe2x80x9cLocation Managementxe2x80x9d, which in this text is called position management. Position management requires signalling via radio, which consequently implies that a certain part of the total radio capacity in a cellular system is needed for this type of signalling, which here for the sake of convenience is called position signalling. In order to make most possible share of the limited radio capacity possible to use for voice respective data traffic, the position management must be optimized so that it takes a minimum of the available radio resource. The degree of difficulty of the optimizing problem is increased by the fact that the mobile stations are just, as the name indicates, mobile.
In prior art the strategy for position management is to find a suitable compromise between signalling in uplink, i.e. from the mobile station to one in the mobile system permanent installed network of base stations, and signalling in downlink, i.e. from the network of base stations to a mobile station. Signalling in downlink is normally executed by searching, also called xe2x80x9cpagingxe2x80x9d, whereby a signalling message is transmitted from the network, to search for a mobile station in a limited area, a so called xe2x80x9cRouting Areaxe2x80x9d (RA) which consists of one or more cells. Signalling in uplink is executed by a mobile station at intervals transmitting a message to the network, which by that can keep count of where the mobile station is at the moment. Updating of the position of the mobile station is made on one hand at change of cell, which is called xe2x80x9cCell Updatexe2x80x9d (CU), and on the other at change of Routing Area, which in its turn consequently is called xe2x80x9cRouting Area Updatexe2x80x9d (RAU).
In a mobile telephone system which supports packet switched services, for instance according to the specification which in English is called General Packet Radio Service and is abbreviated GPRS, the capacity and the radio resource is utilized in a comparatively cost efficient way. This is due to the fact that a given GPRS mobile station utilizes a radio channel only when there are data that shall be transmitted or received by this mobile station. In GPRS there are specified three states of a mobile station. i.e. xe2x80x9cIdle Statexe2x80x9d, xe2x80x9cReady Statexe2x80x9d and xe2x80x9cStandby Statexe2x80x9d, at which there are different operations for position management at each of the different states. In the Idle State, the mobile station is not connected to the network, and the network therefore has no information about the position of the mobile station. When the mobile station is in Ready State or in Standby State, it can, on the contrary, receive paging messages and it also can execute Routing Area Update (RAU), respective Cell Update (CU).
When the mobile station is in Ready State and it changes cell, a Cell Update (CU) is executed if the cells belong to the same routing area. If the new cell which the mobile station enters into also belongs to a new routing area, a Cell Update (CU) is executed combined with a Route Area Update (RAU). In the Ready State there are in fact two xe2x80x9csub-statesxe2x80x9d. Firstly xe2x80x9cReceive/Transfer Modexe2x80x9d, i.e. receiving/transmission mode, which is the state that usually is used at reception respective transmission of voice respective data traffic. Secondly, xe2x80x9cWait Modexe2x80x9d, which implies one by a time parameter limited waiting state, at which the time parameter indicates a time during which the mobile station shall remain in Ready State/Wait Mode in order to later switch to Standby State. At Standby State only Routing Area Update (RAU) is executed when the mobile station changes routing area.
The signalling load which is to be referred to the position management depends on the size of the routing area, and the time which the time parameter indicates. Within known technology there has since a long time been attempts at minimizing this signalling load by means of optimization of the size of the routing area.
An aim of the invention and the overall problem to be solved is to further minimize the signalling load which depends on he position management. One in this context new problem, which is an aspect of said overall problem, is to determine a time parameter which at each state of the mobile station minimizes the position management depending signalling load.
The invention is based on the understanding that the problem can be solved by setting the value of the time parameter in relation to the speed of a mobile through a cell network.
If the mobile station is stationary or is moving slowly, in the cell network, the time parameter is, according to the invention, set at a comparatively high value. This results in that the mobile station will for a longer time be in the Ready State and no paging need to be executed, because the network knows exactly in which cell the mobile station is. The paging signalling, i.e, the signalling in downlink, therefore is significantly reduced. Because the mobile station is stationary, or only moving slowly, no or very low frequent Cell Updates (CU) are needed, which consequently results in low signalling also in uplink.
If, on the other hand, the mobile station is moving rapidly through cell network, the time parameter is, according to the invention, set at a comparatively small value. This in its turn results in that the mobile station is in Ready State during a shorter time, and instead more rapidly changes into the Standby State. This also results in a lower number of Cell Updates (CU) and, when necessary, Routing Area Updates (RAU) are executed, which consequently results in reduced signalling in uplink.
Consequently the above mentioned problem is solved by the time parameter which controls the time during which a mobile station is in Ready State/Wait Mood being set adaptively depending on the present speed of a mobile station through a cell network.